1. Field of the Invention
This invention relates to a stent for tanned, natural tissue heart valves, to a method for preparing such stents, and to a heart valve prosthesis including the stent.
2. Description of the Prior Art
There are basically two types of heart valve prostheses: mechanical valve prostheses and natural tissure valve prostheses. Recent experience indicates the tissue type may be superior to the mechanical type as regards similarity to natural flow characteristics, thrombogenicity, and incidence of catastrophic in vivo dysfunction.
It is known that the tensile properties and antigenic reaction of natural tissue valves may be improved if they are tanned before being implanted. Glutaraldehyde has been used as a tanning agent. (Yarbrough et al: Structural alterations in tissue cardiac valves implanted in patients and in calves. J Thoracic and Cardiovascular Surgery 65, March 1973, pp 364-74).
Heart valve prostheses desirably include a stent or support in which the valve is held in place. The stents normally comprise a frame covered with a cloth or sponge sleeve. Variously configured frames and various frame materials have been used in an attempt to provide a stent that does not contribute to in vivo valve dysfunction. For instance U.S. Pat. No. 3,570,014 discloses a stent made of an annular bendable tubular framework, portions of which are covered with fabric to provide an attachment site for the valve. The frame is bent to fit the valve. Another tubular framework stent is disclosed in U.S. Pat. No. 3,755,823. That stent is made of spaced annular tube members that carry three deflectable posts. The framework is covered with a fabric sleeve. Carpentier (Human Organ Support and Replacement: Transplantation and Artificial Prostheses. J Hardy, ed, Springfield, Ill, Charles C Thomas, 1971, pp 332-62) reports stented valves in which an attempt was made to make the stent frames anatomical by dimensioning them according to measured inside valve dimensions. Even so, these prior art stents were only partial or poor facsimilies of a truly anatomically configured stent.